In total, there were 183 quakes in Oklahoma with at least a 3.0 magnitude between October 2013 and April 14, 2014.
Between 1978 and 2008, an average of just two quakes registering a 3.0 or greater rattled the state each year. The numbers in Oklahoma began to spike in 2009, with the largest quake in state history occurring on Nov. 5, 2011. That 5.6 magnitude earthquake was centered near Prague, roughly 44 miles away from Oklahoma City, and it was felt in at least 17 states in the United States.
There has been a similar uptick across the country: More than 300 quakes of at least a 3.0 occurred between 2010 and 2012, while there was an average of 21 such events each year between 1967 and 2000, the USGS reports.
These recent changes in Oklahoma’s seismic activity “do not seem to be due to typical, random fluctuations,” according to the USGS. Rather, the increase in quakes stems from wastewater being injected into geologic formations.
A lot of the wastewater injected in Oklahoma as well as states like Colorado, Texas, Arkansas and Ohio is a byproduct of oil and gas production; it is disposed of by injecting it into deep disposal wells. Injecting fluid into these areas, which can decrease fault strength and create a buildup of pressure, leads to what is known as “injection-induced seismicity.” This type of seismic activity was to blame for the record-breaking November 2011 quake near Prague, a study published in the Journal of Geophysical Research earlier this year found.
This map shows just how many quakes have rocked Oklahoma over the last few years. Blue dots represent quakes between 1970 and 2008, while red dots show quakes between February 2009 and the end of April 2014:
Researchers with the Oklahoma Geological Survey have increased the number of monitoring stations in Oklahoma in response to the increased number of quakes. They now operate a total of 32 stations; 15 of these are permanent, while many of the 17 temporary stations were loaned by the USGS.
Bill Leith, senior science adviser for earthquakes and geological hazards at the USGS, said in a statement that he hoped the announcement of this increased hazard would help people in the area improve their earthquake preparedness.
“Building owners and government officials should have a special concern for older, unreinforced brick structures, which are vulnerable to serious damage during sufficient shaking,” he said.